multiple mailchimp opt in forms targeting groups

Hi,
I’ve set up 2 mailchimp opt in forms for 2 separate freebies.
In Mailchimp I’ve created a group with 2 categories (one for each freebie)
When I’m adding a mailchimp form in enfold I want to select from the dropdown the group that corresponds to the right freebie.
Is this possible?
Or do I need a plugin for this?
If Yes:
Do you know which plugin is best?
Thank you!
Lisa